Elongated electron-emission cathode assembly and method

ABSTRACT

This disclosure relates to generating an elongated electron beam curtain with the aid of an elongated tubular cathode structure transversely supported against sagging and distortion from a partially surrounding heat-reflecting thermal barrier channel support, particularly adapted for mounting with Pierce type or other beam-forming electrode structures.

United States Patent 1191 Quintal et a1. 1 51 July 10, 1973 [54] ELONGATED ELECTRON-EMISSION 3,531,678 9/1970 schiggflne 313/341 X BLY AND 3,132,274 5/1964 Ken Jr 313/47 CATHODE ASSEM METHOD 2,111,506 3/1938 Edwards et a]. [75] Inventors: Bertram S. Qumtal, Peabody; Dere 2,100,196 11/1931 Lowry., 313/38 I J. Maynard, Danvers, both of Mass.

[ Assigneei Energy sciences -9 Burlington, Primary Examiner-Ronald L. Wzibert Mass- Assistant Examiner-Paul A. Sacher [22] Filed: May 25, 1972 Attorney-Rines and Rines [21] Appl. No.: 256,887

[57] ABSTRACT [52] 53 g g 3 343 This disclosure relates to generating an elongated elec- [51] Int Cl 7 0136152 b 19/12 tron beam curtain with the aid of an elongated tubular Fieid g' h J 3 313239 3m cathode structure transversely supported against sagc 38 81 ging and distortion from a partially surrounding heatg g V r reflecting thermal barrier channel support, particularly adapted for mounting with Pierce type or other beam- 1 References Clted forming electrode structures.

- UNITED STATES PATENTS 3,551,726 12/1970 Blankenship 313/47 X 14 Claims, 1 Drawing Figure ELONGATED ELECTRON-EMISSION CATHODE ASSEMBLY AND METHOD The present invention relates to electron-emission cathode assemblies and methods, being particularly, though not exclusively, concerned with the production of energetic electron beams of considerable length for such purposes as extended-dimension electron treating or processing through elongated electron gun windows and the like.

Cathodes of somewhat long dimensions have heretofore been constructed in filamentary form, either heated end-to-end, or composited by a plurality of short filaments transverse to the length of the electron gun, which is an application of standardly used electron tube cathode technique. Such devices, while useful in certain applications, are inherently seriously limited in practical length, are subject to serious lack of uniform emission densities therealong, and are difficult to form or transversely spread into an expanded uniform denisty beam as for projection through an elongated electron window.

It is to the solution of this as well as related problems, accordingly, that the present invention is, in a principal measure, directed as one of its objectives.

A further object is to provide a novel electronemission cathode assembly and method that is particularly adapted for electron beam generation over very long previously unattained dimensions, say from more than centimeters to 200 centimeters, more or less, and that can achieve this result with electron optical expansion or spreading into uniform density beam curtains.

" An additional object is to provide a novel electron cathode and gun assembly of more general utility, as well.

Other and further objects will be explained hereinaf ter and are more particularly delineated in the appended claims. In summary, however, from one of its aspects, the invention contemplates an electronemission cathode assembly having, in combination, an elongated tubular conductive member adapted to .become heated to electron emission temperature and provided with a predetermined exposed external electronemissive wall surface; tubular thermal barrier and baffle means of larger cross dimension than the member, insulatingly spaced from and extending along and surrounding the other wall surfaces of th tubular member to reflect heat therefrom back thereto, but open to expose said predetermined wall surface thereof; and

means comprising a plurality of supporting means extending transversely of the tubular thermal barrier and baffle means and the tubular member from which it is insulatingly separated, at regions spaced therealong, the supporting means being insulated from the walls of the tubular member. Preferred details are later set forth.

The invention will now be described with reference to the accompanying drawing, the single figure of which is an isometric view illustrating the same in preferred form, with parts partially broken away to show details of construction.

Referring to the drawing, the cathode is illustrated generally at 2 in the form of an elongated longitudinal square or rectangular hollow tubular metal or other conductive member, though other geometries are also clearly useful. In the preferred embodiment, current is directly applied and passed longitudinally along the walls of the cathode tubular member 2, as schematically illustrated at l, to heat the same to electronemission temperature in order to emit electrons from the bottom exposed outer wall surface 2', downwardly in this configuration, though obviously other orientations may also be employed. The cathode tubular member 2 can also be indirectly heated by an internal heater, such as a filament within the tubular member 2, or an external heater, or by a heat pipe at an end thereof, or otherwise, to bring the electron-emitting wall 2' to electron emission temperature.

Partially surrounding the tubular cathode member 2 on its sides 2" and upper wall 2" is a downwardly positioned open-bottom U-shaped tubular channel thermal barrier and baffle assembly comprising an inner conductive tubular channel 6 along the external walls of which thermal insulation 8 is disposed, and an outer U- shaped tubular channel 1. In preferred form, the thermal insulation 8 comprises multifoil layers of thin tantalum or tungsten and the like separated by high temperature dielectric material such as boron nitride and the like.

The inner walls of the tubular channel 6 are shown isolated or separated by an insulator spacer 4 from the current-carrying side walls 2" of the tubular cathode 2, and the upper wall is space-insulated from the upper current-carrying wall 2" of the cathode 2. The inner side walls of theouter tubular channel 1, at least in part, contact the thermal insulation layers 8, and are shown spaced thereabove at the upper wall. A plurality of supporting posts 16-17, positioned at successive locations longitudinally along the elongated cathode 2, support the cathode against sagging or other distortion in use (so common with the filamentary cathode approach) from the thermal barrier and baffle channel structure l-86, with the posts themselves also being insulated from the currentcarryi'ng walls of the cathode 2 by the portion of the insulator 4 that extends transversely therethrough. By this construction, the thermal barrier structure may be maintained at ground or some other reference potential, with complete electrical isolation from the cathode 2.

In operation, it has been found. that the heat generated from the side walls 2" and upper wall 2" of the cathode 2 as the current passes therealong in the preferred embodiment, or as it is otherwise heated, is radiated within the thennal barrier and baffle channels 6-8-1 and becomes reflected back, further to intensify the heating and thus electron-emsision of the exposed bottom wall 2', which may be coated externally with a low work function material.

Through this technique and structure, moreover, the

. cathode 2 is readily adapted for use in Pierce-type and other apertured electrode assemblies for field-shaping and beam forming and expsnding purposes. The assem bly is shown, indeed, suspended by supporting bolts 10 from an elongated U-channel structure 12-14 within which it is centered by guide pins 15 and to which correspondingly elongated Pierce-type electrodes 13 and 19, for example, may be conveniently attached below the cathode-emitting surface 2' extending therealong. The electrode 13 is in the conventional knife-edge form and the electrode 19 disposed therebelow and insulated therefrom by the spacer 18, defines the field-shaping aperture for expanding or spreading the cathodeemitted electrons into a uniform density, transversely wide, longitudinal electron beam. curtain for covering an elongated, wide electron window or the like therebelow, schematically shown at W.

As an example, the substantially square cathode tube 2 may be of tantalum or tungsten, with the inner channel 6 also of tantalum and the outer channel 1 of lower temperature stainless steel. In successful structures, the tube 2 has been about one-fourth inch on a side and about 42 inches long, with the outer channel 1 about 0.56 inches on the side. The supporting posts 16 may be of tungsten, and the insulation 4 of hightemperature dielectric boron nitride or the like. The cathode temperature may reach l8O0 t o l2QQfQ in operation, and even up to 2200 C if tungsten is used, all without sagging or other distortion or non-uniformity of emission area, and with the vastly improved efficiency stemming from the thermal barrier and baffle illumination of the cathode member 2 by forcing the heat to flow into the exposed bottom surface 2'. Structures of this construction have been successfully so operated to expand the beam ten to fifteen times the initial V4 inch width of the emitting surface 2'. Through the use of the invention, indeed, one starts with an emitting surface 2' that can be a significant part of the transverse width of the ultimate window, and, indeed, has a significantly larger emitting area than filamentary cathodes, such that it can operate at a lower temperature than such filaments. A suitable low work function coating material for the emitting surface 2' is lanthinum hexaboride, which enables adequate emission current densities such as 100 milliamperes per square centimeter and greater at relatively low temperatures of the order of l400C.

As before stated, other geometries and orientations may be employed, as well as other types of cathode heating and thermal barrier bafiling; all such being considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An electron-emission cathode assembly having, in combination, an elongated tubular conductive member having top, bottom and side wall portions and including means for heating said member to electron emission temperature and provided with an exposed external electron-emissive wall surface substantially U-shaped; along substantially the entire length of one of said wall portions tubular thermal barrier and baffle means of larger cross dimension than the member, insulatingly spaced from and extending along and surrounding the other wall surfaces of the tubular member to reflect heat therefrom back thereto, but open to expose said predetermined wall surface thereof; and means comprising a plurality of supporting means extending transversely of the tubular thermal barrier and baffle means and the tubular member from which it is insulatingly separated, at regions spaced therealong, the supporting means being insulated from the walls of the tubular member.

2. An electron-emission cathode assembly as claimed in claim 1 and in which said open tubular thermal bar-' rier and baffle means comprises an inner conductive tubular channel externally carrying thermal insulation layer means and internally insulated from the walls of said tubular member.

3. An electron-emission cathode assembly as claimed in claim 2 and in which the barrier and baffle means further comprises an outer conductive tubular channel surrounding the thermal insulation layer means.

4. An electron-emission cathode assembly as claimed in claim 3 and in which said supporting means comprise conductive posts that transversely pass through the barrier and baffle means outer channel, thermal insulation layer means, inner tubular channel and internal insulation, and the walls of said tubular member.

5. An electron-emission cathode assembly as claimed in claim 2 and in which the inner tubular channel internal insulation comprises insulating spacer means disposed between portions of the external walls of the surrounded tubular member and corresponding opposing inner wall portions of the inner tubular channel, with an insulating space being provided between other opposing wall portions.

6. An electron-emission cathode assembly as claimed in claim 5 and in which the barrier and baffle means further comprises an outer conductive tubular channel surrounding and contacting portions of said thermal insulation layer means but spaced from other portions thereof.

7. An electron-emission cathode assembly as claimed in claim 5 and in which the tubular member and tubular channel are substantially rectangular in cross section, the exposed predetermined electron emission wall surface of the tubular member is one wall, the said insulating spacer is disposed along the two adjacent side walls, and the insulating space is provided between the remaining wall of the tubular member and the corresponding inner tubular channel wall.

8. An electron-emission cathode assembly as claimed in claim 7 and in which an outer conductive tubular channel surrounds the thermal insulation layer means contacting the same at the side walls but spaced therefrom at the said remaining wall.

9. An electron-emission cathode assembly as claimed in claim 1 and in which the tubular member is of substantially rectangular cross section, and means is provided for passing current along the tubular member walls to heat the same for producing electron emission at said predetrmined wall surface.

10. An electron-emission cathode as claimed in claim 1 and in which a low work function material is provided along said predetermined exposed external tubular member wall surface.

11. An electron-emission cathode assembly as claimed in claim 1 and in which apertured elongated field-shaping electrode means are provided, and means for mounting the same spaced from extending along the tubular member predetermined electronemitting wall surface to form the emitted electrons therefrom into a uniform density elongated expanded electron beam curtain.

12. An electron-emission cathode assembly as claimed in claim 11 and in which said electrode means comprise Pierce-type beam-expansion electrodes.

13. An electron-emission cathode assembly as claimed in claim I and in which the thermal insulation layer means comprises multiple thin metal layers as of thin tantalum and tungsten separated by high temperature dielectric as of boron nitride.

14. An electron-emission cathode assembly having, in combination, an elongated conductive member having top, bottom and side wall portions and including means for heating said member to electron emission temperature and provided with an exposed external electron-emissive surface substantially U-shaped; along substantially the entire length of one of said wall pority of supporting means extending transversely of the thermal barrier and baffle means and the said member form which it is insulatingly separated, at regions spaced therealong, the supporting means being insu lated from the walls of the said member.

a: a: m a:

Patent No. 3,745,396 Dated y 10, 1973 Inventor(3) Bertram Quinta! and Derek J. Maynard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 2, line l should read the exposed outer surface 2' of the bottom wall portion, downwardly Line 13 should read on its side wall portions 2" and upper wall portion 2" is a downwardly posi- Line 23 should read The inner surfaces of the walls of the tubular channel 6 are shown Line 25 should read current-carrying side wall-portions 2'. of the tubular cathode 2,

Line 27 should read current-carrying wallportion 2" of the cathode 2. The inner surfaces of the Line 37 should read insulated from the current-carrying wall POI'lIlLHlS oi the cath- Line 44 should read ated from the side wall portions 2" and upper wall portion 2" of the Line 50 should read bottom wall portion 2", which may be coated externally with a in column 3, the second from the last line of Claim 1 should read means being insulated from the wall portions of the tubular In column 4 the last line of Claim 4 should read tion, and the wall portions of said tubular member.

Claim 5 should read An electron-emission cathode assembly as claimed in Claim 2-and in which the inner tubular channel internal insulation comprises insulating spacer means disposed between opposing regions of the external surfaces of the wall portions of the surround d tubular member and of corresponding inner surfaces of the walls of the inner tubular channel, with an insulating space being provided between other opposing regions of those surfaces.

t Page i of 2 Pages FQRM Po'w50 (10-697 USCOMM-DC 603764 69 U.5. GOVERNMENT HUNTING UFFKIE I 19.9 0"36533L Unitas STAT S PA'IENT ornate CERTIFlCATE OF CORRECTION Patent No. 3, 7 3976 I I Q Dated July 10, 1973 Inventor Bertram S. Q cl and Derek J Maynard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 7 should read An electron-emission cathode assembly as claimed in Claim Sand in which the tubular member and tubular channel aresubstantially' rectangular in cross section, the said insulating spacer means is disposed along the two side wall portions adjacent to said one wall 1 portiomand the insulating space is provided between the remaining wall portion of the tubular memberand the corresponding inner tubular channel Wall. ""0 V Claim 8 should read- An electron-emission cathode assembly as claimed in Claim 7 and'in which an outer conductive tubular channel surrounds the thermal insulation layer means contacting the same at side walls of the outer tubular channel but spaced therefrom at the remaining wall thereof.

In Claim 9, the last twolines should read wall portions to heat the same forprodu cin'gelectron emission at said predetermined Wall surface. I

Signed and sealed this lst day of October 1974.

(SEAL) Attest: I

MCCCY Mt GIBSON I I 7 a I c. MARSHALL DANN attesting Officer I I v Commissioner of Patents 'oRMeo-wsoHo-sr 7 h USCOMWDC 0376*,

UlS, GOVERNMENT PRINTING OFFICE i9! O-366-33 4, 

1. An electron-emission cathode assembly having, in combination, an elongated tubular conductive member having top, bottom and side wall portions and including means for heating said member to electron emission temperature and provided with an exposed external electron-emissive wall surface substantially U-shaped; along substantially the entire length of one of said wall portions tubular thermal barrier and baffle means of larger cross dimension than the member, insulatingly spaced from and extending along and surrounding the other wall surfaces of the tubular member to reflect heat therefrom back thereto, but open to expose said predetermined wall surface thereof; and means comprising a plurality of supporting means extending transversely of the tubular thermal barrier and baffle means and the tubular member from which it is insulatingly separated, at regions spaced therealong, the supporting means being insulated from the wall portions of the tubular member.
 2. An electron-emission cathode assembly as claimed in claim 1 and in which said open tubular thermal barrier and baffle means comprises an inner conductive tubular channel externally carrying thermal insulation layer means and internally insulated from the walls of said tubular member.
 3. An electron-emission cathode assembly as claimed in claim 2 and in which the barrier and baffle means further comprises an outer conductive tubular channel surrounding the thermal insulation layer means.
 4. An electron-emission cathode assembly as claimed in claim 3 and in which said supporting means comprise conductive posts that transversely pass through the barrier and baffle means outer channel, thermal insulation layer means, inner tubular channel and internal insulation, and the wall portions of said tubular member.
 5. An electron-emission cathode assembly as claimed in claim 2 and in which the inner tubular channel internal insulation comprises insulating spacer means disposed between portions of the external walls of the surrounded tubular member and corresponding opposing inner wall portions of the inner tubular channel, with an insulating space being pRovided between other opposing wall portions.
 6. An electron-emission cathode assembly as claimed in claim 5 and in which the barrier and baffle means further comprises an outer conductive tubular channel surrounding and contacting portions of said thermal insulation layer means but spaced from other portions thereof.
 7. An electron-emission cathode assembly as claimed in claim 5 and in which the tubular member and tubular channel are substantially rectangular in cross section, the said insulating spacer means is disposed along the two side wall portions adjacent to said one wall portion, and the insulating space is provided between the remaining wall portion of the tubular member and the corresponding inner tubular channel wall.
 8. An electron-emission cathode assembly as claimed in claim 7 and in which an outer conductive tubular channel surrounds the thermal insulation layer means contacting the same at side walls of the outer tubular channel but spaced therefrom at the remaining wall.
 9. An electron-emission cathode assembly as claimed in claim 1 and in which the tubular member is of substantially rectangular cross section, and means is provided for passing current along the tubular member wall portions to heat the same for producing electron emission at said predetrmined wall surface.
 10. An electron-emission cathode as claimed in claim 1 and in which a low work function material is provided along said predetermined exposed external tubular member wall surface.
 11. An electron-emission cathode assembly as claimed in claim 1 and in which apertured elongated field-shaping electrode means are provided, and means for mounting the same spaced from and extending along the tubular member predetermined electronemitting wall surface to form the emitted electrons therefrom into a uniform density elongated expanded electron beam curtain.
 12. An electron-emission cathode assembly as claimed in claim 11 and in which said electrode means comprise Pierce-type beam-expansion electrodes.
 13. An electron-emission cathode assembly as claimed in claim 1 and in which the thermal insulation layer means comprises multiple thin metal layers as of thin tantalum and tungsten separated by high temperature dielectric as of boron nitride.
 14. An electron-emission cathode assembly having, in combination, an elongated conductive member having top, bottom and side wall portions and including means for heating said member to electron emission temperature and provided with an exposed external electron-emissive surface substantially U-shaped; along substantially the entire length of one of said wall portions elongated thermal barrier and baffle means of larger cross dimension than the member, insulatingly spaced from and extending along and surrounding the other surfaces of the member to reflect heat therefrom back thereto, but open to expose said predetermined surface of the member; and means comprising a plurality of supporting means extending transversely of the thermal barrier and baffle means and the said member form which it is insulatingly separated, at regions spaced therealong, the supporting means being insulated from the walls of the said member. 